It is well known that engine parts, particularly the blades of the turbine of aircraft gas turbine engines are cooled by use of engine cooling air. For example, cooling of the turbine blades is attained by routing cooling air from the engine's compressor through a TOBI (turbine on-board injector) which is then fed through internal passages formed within the blade. The air is ultimately discharged through openings in the turbine blades and may be returned to the engine's gas path.
Equally well known is the fact that foreign matter, either acquired through the ambient environment or self-generated within the engine, ingests into the cooling airstream and has the propensity of clogging these cooling passages and openings referred to in the above. Obviously, aircraft that is operating in areas where dust is at high levels, such as in the sandy areas of certain geographic locations of the world, the problem becomes exasperated.
Many attempts have been made to alleviate these problems and examples of such attempts are disclosed, for example, in U.S. Pat. No. 3,356,340 granted to M. Bobo on Dec. 5, 1967, U.S. Pat. No. 4,309,147 granted to W. E. Koster et al on Jan. 5, 1982, U.S. Pat. No. 2,632,626 granted to F. A. McClintock on Mar. 24, 1953 and U.S. Pat. No. 3,918,835 granted to G. J. Yamarik on Nov. 11, 1975, the latter two patents being assigned to United Technologies Corporation, the assignee of this patent application.
In each of these instances the cooling air passes through a tortuous route before reaching the turbine cooling passages so that the foreign particles in the cooling airstream are diverted from the turning cooling airstream or the cooled air entrained dirt is admitted to a centrifugal field where the heavier foreign particles are centrifuged to a surface and retained there until the engine is disassembled and cleaned. The U.S. Pat. No. 3,918,835 discloses a centrifugal type of dirt separator and provides an inclined surface that directs the collected dirt particles toward the labyrinth seal where it migrates thereto and is carried through the seal by the leakage air.
In other types of dirt separators or removal schemes, mechanisms upstream of the turbine are provided so as to prevent the dirt from reaching the turbine blades. Historically, such schemes would include a ramp mounted ahead of the TOBI. The ramp serves to deflect and prevents the dirt from making the sharp turn that is require for the cooling air to get into the TOBI. This has met with some success where the dirt particles are sufficiently large so that the inertia of the particle overcomes the velocity of the cooling airstream causing the particle to continue its travel while the air makes a turn. However, smaller sized particles would be influenced by the cooling stream velocity and would turn with the air and hence be carried into the blade cooling passages and holes. This resulted in dirt buildup in passages and clogging of holes which adversely affected the cooling ability of the cooling system. Obviously, this blockage can result in distress or failure of the airfoil or reduce the pressure of the cooling air supplied to the vane upstream of the turbine. To overcome the pressure loss it would be necessary to increase coolant outflow which, in turn, would increase the burner pressure drop and thereby adversely affect engine performance.
We have found that we can obviate the problems enumerated in the above by designing the blade itself to carry its own dirt removal system, hence providing a method to make the cooled turbine blades tolerant to dirt or dust contaminating the cooling air. Inherently, such a system would eliminate the need of the upstream air cleansing schemes that have been heretofore prevalent in the gas turbine engine technology.